Wireless communication devices, such as WIFI 802.11N and LTE compliant communication devices, are increasingly using Multiple Input-Multiple Output (MIMO) antenna technology to provide increased data communication rates with decreased error rates. A MIMO antenna includes at least two antenna elements.
MIMO technology may offer significant increases in data throughput and/or transmission range without the need for additional bandwidth or transmit power. It can achieve this due to the ability of MIMO to obtain higher spectral efficiency (more bits per second per hertz of bandwidth) and/or reduced fading.
MIMO based systems allow the use of a variety of coding techniques that take advantage of the presence of multiple transmit and receive antennas. For example, wireless communications performed over a MIMO channel can use beamforming, spatial multiplexing and/or diversity coding techniques.
The operational performance of a MIMO antenna depends upon obtaining sufficient decoupling and decorrelation between its antenna elements. It is therefore usually desirable to position the antenna elements far apart within a device and/or to use radiofrequency (RF) shielding therebetween while balancing its size and other design constraints.
Correlation between antennas can also be reduced by causing the antennas to have different polarizations, i.e. sending and receiving signals with orthogonal polarizations. Furthermore, antennas for MIMO systems may utilize spatial separation, or physical separation, to reduce correlation between antennas.
Mobile terminals may need to cover multiple-bands in Long Term Evolution (LTE) environments. Antenna systems may, therefore, be required to cover up to seven different frequency bands, for example. In addition, the antenna systems may be required to meet the requirements of Single Input-Single Output (SISO) and Single Input-Multiple Output (SIMO) for 3GPP and 2G bands. The antenna configuration will generally be required to fulfill Specific Absorption Rate (SAR) requirements and other industry standards as well. User effects, such as the way a user holds a mobile terminal relative to the positioning of the antenna elements therein may affect the over the air performance of the device.